Studies on the abscission of the apices of long shoots and short shoots and adventitious abscission of internodes in mulberry (Morus alba)

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Previous work established that shoot-tip abscission following the cessation of apical growth could be induced in diffrent internodes in mulberry (Morus alba L.cv. Shin-incinose).1. The present study has shown that the removal of the apices of the lateral, short shoots of 1-year-old stems of low-pruned trees (decapitation) caused adventitious abscission of the distal internodes and that the abscission was delayd by treating the cut surfaces of the internodes with lanolin paste containing 500ppm auxin (1-naphthaleneacetic acid ; NAA) or painting the distal internodes with 100, 500ppm NAA in aqueous solution, using absorbent cotton. Similar decapitation-induced, adventitious abscission of the distal internodes of the upper, long shoots of 1-year-old stems of low-pruned trees also occured, and application of 100, 500ppm NAA in aq. soln. to the distal internodes of the decapitated, long shoots delayd the abscission. In contrast, application of 100, 500ppm Ethephn in aq. soln. to the distal internodes stimulated the abscission. The results suggest that auxin and ethylene are involved in the control of the adventitious abscission of internodes in mulberry, as demonstrated for the leaf abscission.2. Training 1-year-old stems of low-pruned stumps of mulberry (Morus alba L.cv. Shinichinose) horizontally (arching) before spring bud-burst resulted in a remarkable inhibition of the development of buds on the lower side which remained dormant or grew only into spur buds or poor short shoots, causing the abuscission of spur buds and short shoots. This inhibitory effect was found to be a gravimorphic one, by the removal of the buds on the upper side of the arched stems before spring bud-burst. Thus in these debudded, arched stems, there was a delay in the sprouting of the buds on the lower side as in the case of the buds on the lower side of the untreated arched stems.